It is well known that contact lenses can be used for cosmetics and the correction of visual acuity. The ideal contact lens is one which is not only comfortable to wear for extended periods of time, but also easily manufactured at minimum cost.
Currently, a casting molding process is one of the most cost-effective manufacturing processes for production of contact lenses. A number of lens-molding processes have been reported, for example, PCT patent application no. WO/87/04390 or in EP-A 0 367 513. In a typical molding process, a predetermined amount of a polymerizable or crosslinkable material is dispensed in the female mold half of a mold and the mold is closed by placing the male mold half proximately to the female mold half to create a cavity having a desired geometry for a contact lens. Normally, a surplus of polymerizable or crosslinkable material is used so that when the male and female halves of the mold are closed, the excess amount of the material is expelled out into an overflow area adjacent to the mold cavity. The polymerizable or crosslinkable material remaining within the mold is polymerized or cross-linked with the delivery of radiation thereto through UV light, heat action, or other non-thermal methods. Since the geometry of the ophthalmic lens is specifically defined by the cavity between the male and female mold halves and since the geometry of the edge of the ophthalmic lens is defined by the contour of the two mold halves in the area where they make contact, a contact lens is manufactured into a final form between typically male and female mold halves, with no additional finishing work on the surface of the lens or the edges of the lens. Such full-mold process can reduce cost in the production of contact lenses.
However, In a typical molding process, a contact lens, which is removed from the mold after curing, needs to undergo the other manufacturing processes such as hydration/extraction and sterilization, which can increase manufacturing cost of contact lenses. To overcome this problem, an improved contact lens-molding process is developed and described in U.S. Pat. Nos. 5,508,317, 5,583,463, 5,789,464, and 5,849,810. By using a prepolymer which is a water-soluble photo-crosslinkable polyvinyl alcohol, a finished lens of optical quality can be produced in a mold within a few seconds without the necessity for subsequent extraction or finishing steps to the contact lens. With such manufacturing process, contact lenses can be manufactured at a reduced cost and thus it is possible to produce disposable contact lenses that are discarded by the user after a single use.
Although each of contact lens-molding processes in the prior art is able to reduce manufacturing cost of contact lenses to some extends, cost associated with molds and production thereof can be relatively high. Partly because of the relatively-high cost associated with use of molds and partly because of difficulty in managing an inventory with a huge number of SKUs, a family of contact lenses made by a lens molding process generally can only have a limited number of variations in optical power and/or choices of base curve and/or the like. In most cases, a patient has to use contact lenses which would have closes match to his (her) prescription or use customized contact lenses which are expensively produced, for example by lathing.
Morever, in a typical molding process, the dispensing of a predetermined amount of a polymerizable or crosslinkable material into one of the two mold halves could be a challenging manufacturing issue. For example, the viscosity of the polymerizable or crosslinkable material has to be within a certain specific value so that it would be possible to dispense the polymerizable or crosslinkable material at a reasonable cost. Also, one has to take all possible measures to eliminate the formation of bubbles during dispensing of the polymerizable or crosslinkable material. All the above-stated manufacturing issues and others related to dispensing of the polymerizable or crosslinkable material can increase the cost for producing contact lenses and also limit the choices of available polymerizable or crosslinkable material for making contact lenses.
Therefore, there still exists a need for a new method for economically producing contact lenses without using molds. There also exists a need for a cost effective method of producing customized contact lenses.